4D laser camera for accurate patient positioning, collision avoidance, image fusion and adaptive approaches during diagnostic and therapeutic procedures
(a) The scanned laser fan beam emerges from the upper front end of the LC system while the camera that records its intersection with the patient surface is located at the lower distal end of the unit. The dash dotted lines show the camera and the laser lines field of view, which in turn defines the maximum detectable volume for patient imaging, (b) Most diagnostic equipment and the planned fast IMRT unit shown here will use a more closely integrated LC system with the camera and laser mounted at the opposite sides of the cylindrical opening. (c) Close up of the optical triangulation method showing the fan shaped laser beam and the associated patient profile seen by the recording CMOS camera. This figure describes the internal optical geometry in the treatment units of (a) and (b) or any diagnostic unit similar to (b).
(a) Illustration of the position of the laser beam in relation to the gantry of the Race Track accelerator at Karolinska University Hospital in Stockholm. (b) All points on the contours are calculated by optical triangulation. Several contours then form a surface with a geometrical resolution determined by the distance between the individual contours and the CMOS-camera pixel density.
The upper panel shows a scan of a flat object in the plane with three tape layers of thickness , 0.25 and located at approximately 20, 50 and along the axis, respectively. The width and length of the markings are and . The lower panel shows a thickness profile through the surface in the plane where the object of thickness is clearly detectable by the LC system.
The plot shows the variation of the mean height of a single contour at a fixed position as the patient was holding his breath. The amplitude is the patient’s heartbeat and the slow drift is caused by air that may leak out or slow muscle movements during the breath hold.
A 2D digital photo (top right panel) is mapped on to the 3D LC surface (top left panel) making it possible to view the patient from any direction as shown in the lower panel. This method could also be used to describe the entrance portals in 3D on the patient by turning on the light field with the patient in place and using the CMOS camera to photograph the patient view without the laser turned on and then project the image on the 3D laser camera view.
The reference surface and the real time surface in the right panels are displayed in different colors or shades of gray to visualize the positioning error. The relative correction is the deviation between the surfaces while the absolute correction is the new suggested treatment couch coordinates. The lower right panel shows the calculated correction after the patient has been moved according to the couch coordinates in the upper right panel. The arms are very well aligned but a breathing error is still present in the lower right. This type of dynamic setup error can be eliminated by synchronizing the dose delivery with the real time patient position seen by the LC system or by excluding parts in the abdominal region.
PET-CT-LC. The top left picture displays the height differences, detected by the LC system, of the chest contour. It is color coded such that blue means below average (exhale) and red means above average (inhale). The right picture shows a combined PET-CT image where the breathing artifacts are visible as multiple peaks on the skin surface at the left side of the image.
In Vivo dose delivery imaging using PET-LC imaging. The patient has been scanned during a radiotherapy treatment and then immediately transported to a PET camera in order to detect the delivered dose distribution in reference to the patient surface. The lower part of the patients skin is made semitransparent to show the entire PET detected photo nuclear generated dose distribution and the approximate location of 30%, 50% and 80% isodoses are also indicated.
Use of an Anatomic lymph node atlas (green) warped to fit to the individually observed involved lymph nodes (orange to yellow) during PET-CT imaging. This will allow a more accurate selection of the target volume in radiation therapy since there are often involved sub clinical lymph nodes not visible on PET that need to be included in the clinical target volume.
Rigid body positioning accuracy using treatment couch translation.
Translational and rotational deviations from day to day of a patients’ position as detected with the LC system.
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